Response of ultrasound contrast agents to static overpressure.

Abstract

This study investigated the static pressure threshold for contrast agent (CA) rupture. Polymer-shelled CAs (mean diameter of 3 μm) with a constant shell-thickness-to-radius ratio (STRR) were subjected to overpressure in a cylindrical test chamber containing an optical window on its top and bottom faces. A video-microscope (50× magnification, 128 μm FOV, 1 Mpixel CCD) was used to image the CAs while static pressure was increased from 0.5-22 psi by pumping water into the chamber at a constant flow rate. An image processing algorithm was used to determine the change in diameter as a function of static pressure for each CA (total of 130). The majority of CAs did not respond to static overpressure until the threshold for shell rupture was exceeded, resulting in abrupt destruction. The probability density function of rupture pressures exhibited four lobes and four subsets that were obtained by a k-means algorithm. Measurements indicated that mean rupture pressures in each group were independent of CA diameter. This observation is in agreement with the classical theory for a perfectly spherical shell, which predicts that the critical compression load is a function of STRR and not of the diameter alone. [Work supported by NIH EB006372.]